Many transmitters transmit digital information values that are generated in base band. The base band digital values are modulated onto a carrier high frequency signal and the combined signal is amplified before its transmission. The base band values may be complex values having real and imaginary components which arc traditionally referred to as I and Q components, respectively. In the modulation of the base band signal and amplification of the modulation signal, inaccuracies are introduced. These inaccuracies may cause the transmitter to interfere with signals on carrier frequencies allocated to other transmitters and therefore should be at least partially canceled by the transmitter.
One of these inaccuracies, which is due mainly to an IQ modulator of the transmitter, is referred to as IQ mismatch which is generally modeled by the following equation:                                           V            _                    q                =                              (                                                                                I                    q                                                                                                                    Q                    q                                                                        )                    =                                    [                                                                                          cos                      ⁡                                              (                        φ                        )                                                                                                                        sin                      ⁡                                              (                                                  -                          φ                                                )                                                                                                                                                        b                      ⁢                                                                                           ⁢                                              sin                        ⁡                                                  (                                                      -                            φ                                                    )                                                                                                                                                b                      ⁢                                                                                           ⁢                                              cos                        ⁡                                                  (                          φ                          )                                                                                                                                ]                        ⁢                                                   ⁢                          (                                                                                          I                      d                                                                                                                                  Q                      d                                                                                  )                                                          (        1        )            in which Id, Qd are the real and imaginary input base band values of the modulator, Iq, Qq are the real and imaginary base band equivalent output values of the modulator and (φ,b) are constants which describe the IQ mismatch of the modulator. This inaccuracy may be compensated for by a mismatch correction multiplier. It is required, however, to estimate the parameters of the mismatch correction multiplier.
Another inaccuracy is due to the non-linearity of the amplification of thc transmitted signal. The non-linearity may be compensated for by a predistorter.